Automatic telephone exchange system



June 30, 1931. A. F. DIXON AUTOMATIC TELEPHONE EXCHANGE sYs'pEM 1i SheecsfSheet 1 [IHII Filed Jan. 6, 1950 ATTORNEY Jun 30, 1931. A. F. DIXON AUTOHATIC TELEPHONE EXCHANGE SYSTEM 11 Sheets-Sheet 2 Filed Jan. 6, 1930 /N\/ENTO/? AJTD/XO/v QrM A TTUHNE) J=m mm June' 30, 1931. A. F. WON 1 11,844

AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. 6, 1930 ll Sheets-Sheet 3 /NVENTL7R Af'U/xmv Q-bM A TTURNEI) June 30, 1931. A. F. DIXON AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. 6, 1930 ll Sheets-Sheet 4 A TTUENEV June 30, 1931. A. F. DIXON 1,811,844-

I AUTOMATIC TELEPHONE EXHANGE SYSTEM Filed Jan. 1950 11 Sheets-Sheet 5' EMF/Z50 /NVE/VTUR A-FU/XON 5y A 7' TURNEV June 30, 1931. A. F. DIXON 1,811,844

AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. 6, 1950 11 Sheets-Sheet 6 //v VENTO/P DIXON BY $12M ATTORNEY June 30, 1931. A. F. DIXON 1,811,844

I AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. 6, 1950 11 Shegts-Sheet 7 v. ATTORNEY "wan/Na JFLECTUR DD- EJ- I E 05 June 30, 1931. I A. F. DIXORE 5 9 AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. 6, 1930 11 Sheets-Sheet 8 MARE/NAIL ATTQRA/f y June 30,1931. A. F. DIXON 1,811,844

AUTOHAT I O TELEPHONE EXCHANGE S YS TEM A TTUHNEY June 30, 1931. A. F. DIXON AUTOMATIC TELEPHONE EXCHANGE SYSTEM 11' Sheets-Sheet 10 Filed Jan. 6, 1930 QQ MNQ M\%\ lNl/ENTUR ALFD/xmv Q-C/M- TTORNEY June 30', 1931. A. .F. DIXON AUTOMATIC TELEPHONE EXCHANGE SYSTEM 11 Sheets-Sheet 11 Filed Jan. 6, 1930 mbm Q wuQk W wutk /N VE N 70/? A. I? Dlxolv BY maamw A TTOENE Y Patented June 30, 1931 UNITED STATES PATENT Mme AMOS F. DIXON, OF JERSEY CITY, NEW JERSEY, ASSIGNOR TO BELL TELEPHONE LAB- V ORATORIES, INCORPORATED, OF NEW YORK N Y., A CORPORATIQN F IIEN YORK AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

Application filed January 6, 1e3o:"seria1 No. 418,861.

The invention relates to an automatic tele: phone system and more particularly to a novel method and system of circuits for utilizing equipment located in one exchange 5 in a large exchange area as overflow or auxiliary equipment for another exchange in the same area.

Where there is a large number of telephone lines to be served as is the case in most cities, these lines are divided among a number of exchanges or offices which together form what is known as an exchange area. The number of oflices, of course, is determined by the geographical distribution of the subscribers 16 to be served and by thedensity of the tele-' phone development in a given section.

It generally occurs that certain of these oflices will serve lines which are used almost exclusively for business purposes and others will serve lines which are used fora variety of purposes other than those classed as strictly business. In olfices where business lines predominate, the peak load is during ordinary business hours and after business hours the load may drop 05' to practically nothing, whereas in the residential districts the peak load is often after business hours. There may be other local conditions which would cause the peak load in the various oflices to occur at different times during the day. For example, reference may be'made to the situation in New York city where offices serving the financial district in the lower part of the city are practically without load after five oclock, whereas the peak load in an oflice serving the hotel and theatrical district comes on between seven and eight in the evening.

It is the usual practice in ofiices which are worked on an automatic basis to provide sufficient equipment in the way of line finders,

selectors and control equipment to take care.

of the peak load. A certain percentage of this equipment is idle when the load is atits minimum. Apparatus which is idle is vnot worked'at a maximum efficiency and fixed charges and depreciation are present whether the equipment is operating or not.

In'accordance with the present invention, advantage is taken of the fact that the peak loads in oneor more ofl ices are at difierent hours of the day and makes equipment in certain ofiices during their period of light load available for handling calls incoming to an otfice operating at a peak load. As a result, it is not necessary to install in the office which is to be assisted, equipment necessary to handle its peak load. These economies are effected both in the initial amount of equipment installed and in the more efficient use of the equipment that isinstalled.

More specifically, in accordance with the invention it is proposed to connect linefind-- ers in one otficc or exchange with the selector switches and control apparatus of another office by means of trunk conductors normally used for handling the calls between the offices. Fora specific example reference may be made to the Hanover and Pennsylvania offices of "New York city wherein the Hanover ofiice serves the financial district and the Pennsylvania ofice serves the hotel and theater district. In accordance with the in-, vention the line Ifinders at the Pennsylvania otlice serving incoming calls at that ofiice are not all connected to the selector switches at the Pennsylvania olfice. A certain numberof these line finders at the Pennsylvania office are connected by interoffice trunks to the selector switches at the Hanover ofiice. Those calls incoming at Pennsylvania which normally would be handled by the line find ers and selector switches-of the Pennsylvaniaoti icevare routed to Hanover and handled through the equivalent equipment at the Hanover office. The arrangement is such that this routing may be made efiective only during the hours of peak load at the Pennsylvania office and the hours of light load at the Hanover ofiice. By utilizing selector switches and controlapparatus at the H'anover oflice, an equivalent amount of control equipment and selector switches is released at the Pennsylvania office for other use or. a corresponding amount of 'equipment may be omitted from the Pennsylvania oifice.

In accordance with a feature of this invention a switching arrangement is provided whereby certain of the line finders in one oflice may becswitched into association with the selector switches at another office. This switching means may be either manually controlled or automatically controlled in accordance with the amount of traffic. In one case, the second otfice would take care of a certain portion of the incoming traffic at the first ofiice when the switching apparatus'has been operated, whereas in the other case a variable amount of the traffic would be handled at the second oflice dependingupon the busy or idle condition of the apparatus at the first office.

It is apparent that in accordance with the present invention the capacity for incoming calls at a given ofiice may be materially increased without increasing the equipment other than adding the necessary number of line finders. he rest of the equipment 1s. operative from another oflice during the perriod of peak load.

. A clearer conception of the scope and purpose'of the invention may be obtained from. a consideration of'the following descriptionv in connection with the attached drawings in e which Figs. 1 to show apparatus at an office A of an exchange system and Figs. 6 130-10 show apparatus at an o-fliceB of the same exchange;

Fig. 1 shows a calling subscribersline together with relay equipment common to a group of lines;

Fi 2 shows a start circuit;

Fig. 3. shows a line finder and district. selector;

Fig. 4 shows a: link circuit for associating; a sender, diagrammatically illustrated, with the district selector of Fig. 3;

Fig. 5 shows a line finder having access to the calling line for serving such calling line during periods of peak load and associable with a. district selector, Fig. 8, of office B;

Fig. 6. shows a calling subscribers line together with common relay equipment termi-- nating in office B;

Fig. 7 shows a start circuit;

Fig. 8 shows a line finder andzdistrict selector, the district selector being arranged to be paired with the line finderof Fig. 5,

and in the lower right portion a representation of alinefinder-district which may be used onlyfor calls locally originated;

Figs. 9 and 10 show link circuits for associating senders, diagrammatically illustrated, with the district selectors of F ig; 8;

Fig. 11 is'a diagram showing how the'several figures should be arranged to illustrate the completecircuits of the invention; and

Fig. 1-2 is a schematic drawing illustrating the principles of the invention.

The invention has been embodied in a dis closure which is substantially like that of Patent No. 1,690,206 granted to. A.. Raynsford, November 6,. 1 928. The senders diagrammatically indicated by the smatl rec'- tangles in the upper left corner of Figs. 4, 9 and 10 are of the character disclosed in the Patent No. 1,589,402 granted to O. H. Kopp, June 22, 1926 and reference to the Kopp patent is made for operations not completely described herein.

As in the disclosures of the above mentioned patents, a plurality of link circuits is provided at each exchange oifice arranged to serve a' group of'calling lines and are taken into service in rotation. When a link circuit completes its function it hunts for and associates itself with a district selector which is ready for use and the link and district remain in a suballotted condition until the next link. in the series'has been put into service.

The link circuit is tllQIll'Plli] into an allotted position from which it will be advanced by the initiation of a call and the action ofthe associated start circuit. For example, the trip circuit of Fig. l and start circuit of Fig. 2 are so arranged that only one line of a group of lines may be served at a time and so that there may be cooperation between two subgroupsof' lines to each of which the group of link circuits of Fig. 4 is individual. The details of these functions form no particular part of the present invention and are fully described in Patent No. 1,567,072. granted to WV. H. Matthies, December 29, 1925.

The start circuit of Fig. 2, however, differs:

from the start circuits of the above mentioned patents in that provision is made for' starting a link circuit of an office B in which at the time traffic is light, in the event that at the time when a call is initiated in either of the line sub-groups of Fig. 1 the trafiic is so heavy that there are no links and senders available in ofiice A for serving the call. At such periods of'peak load the keys shown in the lower right portion of the start circuit of Fig. 2 will beoperated to. their alternate positions and the key shown in the upper right portion of Fig. 5 will be operated to associate' the linefinder of Fig. 5 with an interoifice trunk extending to a district selector in office B. When such a condition arises a call is transferred to the start circuit of Fig. 7, and apreallotted link, Fig. 10, of oii'ice B is started to select a sender and to associate it with av district selector of oitfice B for serving the call.

In addition, the start,'link and district.

selectors of office B'shown in 7, 9 and 8 are modified by the addition of keys which enable this apparatus to be made available for. serving calls originating in oliice A during periods of light load in office B. The keys. associated with the district selector of Fig. 8 are applied only to a portion ofthe district selectors of the frame and when operated disassociate such selectors from their normal association with line finders of office B and associate them with special line finders such as shown in: Fig; 5 in the-same fram'e'as.

calling lines shown in Fig. 1 of officeA.

Referring particularly to Fig. 12 in which apparatus of two oilices A and B of an exchange system have been schmetically illustrated, it will be assumed that ofiic-e A is an office in which a peak load may occur at a time when the load in office B is light. In oflice A the line finders 300 serving the group of subscribers lines are shown paired with districtselectors 350, the line finders in the left half of the line finder frame being arranged to be started through the start circuit 250 and a preallotted link of the A group of link circuits 1200, and the line finders in the right half of the frame being arranged to be started by a link in the B group 1201' in accordance with the practice set forth in the above mentioned patents. In accordance with this invention each half of the line finder frame is also equipped with certain line finders which are linked over interoflice trunks of the trunk group 555 with certain district selectors 890 in the district selector frame of oflice B.

At the ofiice B all of the line finders in both halves of the line finder frame are paired with selectors of the district selector frame during periods of normal load. The line finders of the left half of the line finder frame are arranged to be started through thestart circuit 7 and a preallotted link of the A group of link circuits, and the line finders of the right half of the frame are arranged to be started through the start circuit 750 and a prealloted link of the B group of link circuits. During such normal load periods with the keys illustrated in their normal positions,

all of the apparatus of ofiice' B is effective.

only for handling calls originating in such oflice.

- When, however, a period of light load oc ours in the ofice B and a period of peak load occurs at the same time in the A office, the attendant at ofiice B by operating the keys indicated may render the district selectors 890 available for pairing wit-l1 the line finders 550 of office A over trunks 555 and may transfer the start leads of half of the link circuits of both A and B groups from their normal connection with the startcircuit 7 50 to the start circuit of office A over trunks 983 and 1204. If then all of the apparatus of office A available for serving the group of lines illustrated becomes busy, the transfer relay .3O operates transferring the start conductors extending from start circuit 250 from the link start conductors 229 and 1203 extending to the A and B groups of links in oi'iice A to conductors 983and 1204 extending to the A and B groups of links in ofiice Bi Thus on such peak load calls initiated in otfice A the links of ofiice B will function to select an idle sender and associateitwith an allotted district selector in office B to serve such calls.

OaZZs om'ginatz'ng in. ofice A. and served by apparatus in oyfice B Since under conditions of normal load the apparatus of office A functions in the wellknown manner, fully set forth in the patents referred to, it will not be necessary to describe herein in detail the manner in which a call is extended under those conditions. It will therefore be assumed that at the time the subscriber of calling station 100 initiates a call the links and senders which would ordinarily be available for use are busy because of a peak load condition and that during the eX- istence of that condition the keys 221, 222, 223 and 224 are operated. With these keys operated and all of the link circuits of both the A and B groups busy, circuits are established for the relays 225 and 226. The circuit of relay 226 may be traced from battery,

throughthe winding of relay 226, the upper alternate contacts of key 222, conductor 229,

sequence switch contacts 424, 454 and 453 of busy link circuits of the A group to ground. V

A similar circuit will also be efiective for relay 225 over sequence switch contacts of the busy link circuits of the B group.

When the subscriber at substation 100 re moves his receiver from the switchhook a circuit-is closed from battery, through the winding of line relay 101, inner back contact of relay 102, over the subscribers line to ground at the outer contact of relay 102. Relay 101 in operating closes a circuit from battery, through resistance 104, winding of relay 103 to ground at the right contact of relay 101. It also prepares a circuit from battery, through resistance 111'and the right winding of relay 109 in parallel, left front contact of relay 101 to conductor 114 to identify the calling line to the line finders having accessto that line. Relay 103 in opf crating closes a circuit from battery, over'the back contact of relay 201, conductor 130',

right winding of rela' 108, outerright back contact of relay 107', inner right contact of relay 103 to of relay 109.

Relay 108 operates in this circuit and closes a locking circuit for itself from battery, through the right winding of relay 201, conductor 129, over back contacts of relays similar to relay 108 individual to other subgroups of lines appearing before the same line finder, inner left front contact and left winding ofrelay 108 to ground at the inner right back contact of relay 109. Relay 108 closes a circuitfrom ground at its outer right front contact, through the winding of trip magnets 303 and 503 of the line finders of the frame serving the sub-group of lines in which the substation 100 is located to battery in preparation for tripping the proper set of brushes of the line finder. In actual practice but one trip magnet such as 303-would be used for a single brush group of all line finders of the same frame. However, for the sake of clarity a separate trip magnet has been illustrated for each line finder. Relay 201 operates in the locking circuit of relay 108 and in combination therewith closes a circuit from ground, over its outer right contact, conductor 128, left middle contact of relay 108, winding of relay 110 to battery. Relay 110 looks over its right contact to ground at the outer back contact of relay 109 and closes a circuit for starting an allotted line finder.

It has been assumed that there are no idle link circuits available in ofiice A and that an idle link circuit, for example, link circuit 1099 of Fig. 10, oilice B is to be used. The sequence switch 1000 of this link circuit will therefore be standing in position 1 and the sequence switch 800 of the district selector, Fig. 8, preallotted by the link circuit of Fig. 10 will be standin in position 2. At this time since all of the links of ofiice A normally available for serving the group of lines i which the calling line is located are busy, relays 225 and 226, are operated thereby establishing an obvious circuit for relay 280. The operation of relay 110 will therefore close a circuit from ground at its left contact, the out r left contact of relay 108, the inner left contact of relay 10S, conductor 131, left back contact of relay 202, inner left back contact of relay 203, the right front contact of relay 280, conductor 2 1, alternate contact of key 982, conductor 983 lower contacts of cam 1003, brush 1002, terminal 1001, conductor 878, the lower left and upper right contacts of cam 801, winding of relay 802 to battery. Relay 230 locks over its right winding and right contact in this circuit to prevent the opening or the start circuit should a link in office A become available at this time and release either relay 225 or 226.

Relay 802 in operating closes a circuit from battery through the winding of relay 808, alternate contact of key 805, inner right contact of relay 802, right contact of cam 806, outer left front contact of relay 802 to ground at he'lower right contact of cam 80?. it we been assumed that the keys of all linefindcr-district circuits of the frame on which the linefinder-districts shown in Fig. are located have all been operated to their alternate p\ ions for handling peak load calls originating in office A. Relay 808 upon operating establishes a circuit e1:- tending over the conductors and 505 of the interoflice trunl-z, norn'ially used for extending calls from the bank of a district selector in ofiice it. to an incoming selector in office B, but set apart for peak load calls through the operation of key 809 at office B and key 506 at office B, for operating relay 501 associated witn the line finder. Fig. 5,

of ofiice A. This circuit. may be traced from battery, through the winding of relay 501, the lower normal contact of relay 507, the lower alternate contacts of key 506-, conductor 504, the lower alternate contacts of key 809,. the inner normal contacts of relay 810, the upperrback contact of relay 811,. winding of relay 812, the inner upper contactiof' relay 808, the upper back contact of relay 811, the outer normal contacts of relay 810, the upper alternate contacts of key 809, conductor 505, the upper alternate contacts of key 506 to ground at the. upper normal contacts of relay 507. Relays 501 and 812 operate in this circuit, relay 501 closing an obvious circuit for relay 502 and at its right contact establishing a circuit for relay 500 extending from. battery, through the winding of relay 500, commutator segment 508, brush 509, brush 510, commutator segment 511 to ground. at the right contact of relay 501. Relay 500 upon operating closes obvious circuits for the updrive magnet 512 and.

for relay 513. Relay 513 at its front contact closes a locking circuit for itself eX- tending through the winding of relay 51 l to ground at the left back contact of relay 515. Relay 511 being shunted by ground at the contact of relay 500 does not operate in this locking circuit as long as relay 500 remains energized. The line finder of Fig. 5 moves upwardly under control of magnet 512 and since trip magnet 503 is operated the proper set of brushes is tripped.

As soon as the line finder leaves normal, a locking circuit is provided for relay 500 extending from battery through the left contact of relay 500, the back contact of relay 516, commutator strip 517, brush 518 to ground over brush 510, strip 511 and the right contact of relay 501 which holds relay 500 operated. As soon as the commutator brush 519 engages segment 520 a circuit is closed from ground over brushes 510 and 519, segment 520, conductor 40 1-, contact 232 of key 204, inner front contact of relay 201 to conductor 129 and the right winding of relay 201. This circuit shunts the left winding of relay 108 and causes that relay to. release in turn releasing the trip magnet 503. When brush 519 leaves segment 520 the circuit of relay 201 is opened and that relay releases freeing the start circuit of Fig. 2 and releasing relay 802 in the district selector of Fig. 8. hen the line finder brush 521 makes contact with terminal 522 which is connected to conductor 114C and therefore to battery through the right winding of relay 109, a circuit is completed from this battery, through the winding of relay 516 to ground. Relays 109 and 516 operate, relay 516 opening the holding circuit previously traced for relay 500. As soon as the brushes of the line finder become accurately centered on the terminals of the calling line, a second holding circuit'extending from battery, through the winding and left contact of relay 500, over centering strip 523, brushes 509 and 510 to ground, is opened at an insulating segment of strip 523 and relay 500 releases opening the circuit of updrive magnet 512 and removing the shunt ground from the winding of relay 514 which now operates in the looking circuit of relay 513. Relay 514 upon operating opens the circuit of relays 516 and 109, a its outer right contact establishes an obvious circuit for relay 507, at its inner right contact establishes a circuit for the cut-0E relay 102 of the calling line extending. from battery, through the windings of relay 102, conductor 112, terminal 524 and brush 525 to ground, and at its left front contact connects direct ground to brush 521 over the right normal contacts of relay 526, the right front contact of relay 502, commutator strip 517, brushes 518 and 510, strip 511 to groundat the right front contact of relay 501 and after relay 507 operates, to ground at the lower front contact of relay 507. Relay 109 which operated in series with relay 516 opens the holding circuit of relay 110 thereby restoring the relay equipment of Fig. 1 so that another calling line in the same line group may have access to the common start circuit for starting another call. Relay 507 upon operating disconnects ground and the winding of relay 501 from the trunk conductors 505 and 504 and extends these trunk conductors through the windings of relays .527 and 528 over brushes 529 and 530 and terminals 531 and 532 to the conductors of the calling line. Relay 812 in the district circuit of Fig. 8 is maintained energized over the calling line loop due to the transfer" contacts of relay 507 and relay 527 operates in series therewith. Relay 528 being polarized does not receive current in the right direction through its windings to operate at this time. ,Relay 527 upon operating closes at its contacts a new operating circuit for relay 502 for replacing the original circuit opened at the contacts of relay 501 upon the release of that relay.

At the district selector of Fig. 8 upon the operation of relay 812 a circuit is closed ex tending from ground at the contacts of relay 812, over the lower back contact of relay 811 to battery through the winding of relay 813. Relay 813 operates looking over its front contact, through the winding of relay 811 to ground at the upper front contact of relay 808, but relay 811 being shunted as long as relay 812 remains operated does not operate at this time. As soon as relay 802 releases following the finding of the calling line as previously described, a circuit is established for relay 870 extending from'battery winding of relay 870, contacts of key 871, resistance 872, innermost lower back contact of relay 814, right back contact of relay 802, upper contacts of cam 832 to ground at the right contact of cam 833 and opens the circuit of relay 808. Relay 808 releases in turn releasing relay 812 and relay 870 supplies an operating ground for the circuit of relay 811. Relay 811 thereupon operates opening the initial operating circuit of relay 813 and transferring the trunk conductors 505 and 504 from their connection with the winding of relay 812, over back contacts of relay 814 to cams 815 and 816.

At the time relay 802 operated it closed a circuit from ground at the lower right contact of cam 807 over the left front contact of relay 802, lower left contact of'cam 817 conductor-818, terminal 1007 brush 1006 of the link district finder 1010, upper right contact of cam 1008, winding of relay 1009, resistance 1011 to battery. Relay 1009 operates and closes a circuit from battery, through the winding ofsequence switch magnet 1000, upper contact of cam 1012 to ground at the outer right front contact of relay 1009 advancing .link sequence switch 1000 to position 2. \Vhen sequence switch 1000 leaves position 1 relay 1009 releases. In position 2 a circuit is closed from battery, through the winding of relay 1013, right contacts of cam 1014, left back contact of relay 1015 to ground at the lower left contact of cam 1016. Relay 1013 operates closing a circuit from batter through the right winding of relay 1017, the outer right contact of relay 1013 to ground at the right back contact of relay 1015. Relay 1017 in operating closes a circuit from battery, through the winding of updrive magnet 1018 of the sender finder 1020, left contact of cam 1079, outer right contact of relay 1017 to ground at the right back contact of relay 1009. The sender finder moves upwardly under the control of magnet 1018 in search of an idle sender.

Relay 1013 also closes a circuit from battery through the middle winding of relay 1015, upper contacts of cam 1021, right winding ofrelay 1015 to ground at the inner right contact of relay 1013. The current in this circuit, however, is not 'suflicient to operate relay 1015 but does create a flux in the windings of that relay so that it becomes quick to operate when the test circuit is closed. The test circuit extends from brush 1022, upper contacts of cam 1019, left back contact of re lay1009, left winding of relay 1015, lower right and upper left contacts of cam 1021, right winding of relay 1015 to ground at the inner right contactof relay 1013. An idle sender is characterized by battery potential on terminal 1023 and therefore when brush 1022 engages terminal 1023 the above traced circuit is completed and relay 1015 operates quickly closing a locking circuit for itself from battery, through its middle winding, the uppercontacts of cam 1021, its right front contact to ground. It also opens the circuit of relay 1017 which releases to in turn release magnet 1018 and bring the sender finder 1020 to rest on the terminals of the idle sender. The release of relay 1017 in turn releases relay 1013. With relay 1013 released and relay 1015 operated a circuit is closed from battery, through the winding of sequence switch magnet 1000, upper left contact of cam 1076, contacts 1027 of jack 1028, left back contact of relay 1013, left front contact of relay 1015 to ground at the left lower contact of cam 1016 thus advancing sequence switch 1000 to position 3.

As soon as sequence switch 1000 reached position 1% a circuit was established from ground, over the right contact of cam 1029, brush 1078, terminal 1077, conductor 822, the lower left contact of cam 823, the lower left contact of cam 82-1, to battery through'the left winding of relay 825. Belay 825 upon operating with relay 802 released, closes a circuit for advancing sequence switch 800 into position'3. This circuit extends from battery, through the winding of sequence switch magnet 800, the upper right contact of cam 826, the inner right contact of relay 825, the outer left back contact of relay 822 to ground at the lower right contact of cam 807. With sequence switch 800 in position 3, relay 870 is held operated over key 871, resistance 872, the innermost lower back contact of relay 811- to ground at the lower contact of cam 833.

lVhen sequence switch 1000 reaches position 3 a circuit is closed from ground at the sender over terminal 1030, brush 1031, the lower contact of cam 1031, brush 1032, terminal 1033, conductor 819, lower right and upper left contacts. of cam 820 to battery through the upper winding of relay 81 1- and in parallel therewith over the upper right contact of cam 820, through the winding of relay 821 to battery. Relay 81 1 is marginal and does not operate, but relay 8 21 operates although ineffective at this time.

As soon as sequence switch 1000 arrived in position 2% it prepared the pulsing circuit for receiving dialing impulses. This circuit may be traced from the sender, over terminal 1010, brush 1011, the lower contact of cam 1029, brush 1078, terminal 1077, conductor 822, the upper left contact of earn 815, the upper contact of relay 811, thence as tr ced over the calling subscribers line loop returning over the intermediate lower back contact of relay 814:, the winding of supervisory relay 827, the left Contact of cam 816, conductor 828, terminal 1012, brush 10213, the upper contacts of cam 1003, brush 101 1, terminal 1041-5 to the sender. Upon the establishment of the pulsing circuit dialing tone is transn'iitted to the calling line in the well-known mann r to inform the calling subscriber that the sender is ready to receive impulses which he may then send out by manipulating his dial.

Upon the seizure of the sender, battery is removed from terminal 1023, thus releasing relay 1015, which closes a circuit for advancing sequence switch 1000 into position 5. This circuit may be traced from battery through the winding of magnet 1000,;the upper right contact of cam 1076, the left back contact of relay 1015 to ground at the lower left contact of cam 1016. Sequence switch 1000 remains in position 5 throughout the further operation of the sender. As soon asthe calling subscriber has dialed the oflice code digits, the sender establishes a fundamentalcircuit for controlling the district selector of Fig. 8 which may be traced from battery through the left winding of relay 825, the lower left contact of cam 82 1, upper left contact of cam 823, conductor 878, terminal 1001, brush 1002, the up'percontacts of cam 1035, brush 1036, terminal 1037, through the winding of :the stepping relay (not shown) of the sender to ground. Relay 825 energizes inthis circuit and locks over its outer right front contact and the upper right contact of cam 8241 to the fundamental circuit and also closes a circuit from battery through the winding of-sequence sW-itohmagnet 800, upper right contact of cam 826, inner right front-contact of relay 825, outer left back contact of relay 802 to ground at the lower right contactofcam 807. Magnet 800 operates to advance the sequence switch to position 4.

In posit-ions relay 825 closes a-circui't from battery through the winding of updrive magnet 831, the lower contacts of cam 832,'the inner right front contact of relay 825, thence 'to ground att-he lowerlright contact of cam 807. The updrive magnet operates and causes the district selector switch shaft to move upwardly in a'brush-selecting movement. Each time the commutator'brush 830 makes'contact with a conducting segmentof strip 829, a shuntcircuit is established from ground at the right contact of-cam 833, over brush 830 and strip 829, the upper right contact-of cam 823, the upper right contact of cam 82 1, the outer right front contact of relay 825 to the vinding of relay825 for holding this relay operated, but shunting down the sender ste] ping relay. In the well-known manner the operation of the sender stepping relay operates counting relays of the sender until the sender is satisfied as to the district brush selection coded by the oiiice code registers, when the fundamental circuit isopened at the sender thereby permitting relay 825 to release as soon as brush 830 leaves the conducting segment of strip 829 upon which it last rested. The release of relay 825 opens the circuit of the vupdrive magnet 831 and closes a circuit from battery through the winding of sequence switch magnet 800, the right contacts-of cam 8341, the inner rightback contact of :relay 825 to ground as previously traced for advancing the sequence switch into position 5.

Vith sequence switch 800 in position 5, the fundamental circuit is again closed as previously traced, whereupon the stepping relay of the sender and relay 825 again operate, relay locking to the fundamental circuit over the circuit previously traced and closing the previously traced circuit for advancing sequence switch 800 into position 6. As soon as the sequence switch reaches position 5 a circuit is established for the trip magnet 835 extending from battery through the winding of magnet 835 to ground at the lower right contact of cam 836. lVith sequence switch 800 in position 6, the circuit for the updrive magnet 831 is again closed over the circuit previously traced and magnet 831 causes the switch shaft to move upwardly in its groupselection movement. During the initial portion of this movement due to the energization of the trip magnet 835, a set of brushes is tripped for engagement with the terminal bank. As the shaft continues upwardly a shunt circuit is intermittently established from ground at the right contact of cam 833, over brush 837, commutator strip 838, the lower rightand upper right contacts of cam 82%, the outer right frontcontact and left winding of relay 825 tobattery for holding relay 825 operated and for shunting down the sender stepping relay.

At the sender in response to the intermittent operation of the stepping relay, count-- ing relays are operated in the well-known inanneruntil the sender is satisfied with respect to the district group selection coded by the oflice code registers when the fundamental circuit will be opened at the sender, permitting the release of relay 825 as soon as brush 837 engages the next insulating portion of strip 838. -Relay 825 upon releasing opens the circuit of updrive magnet 831 to arrest the upward movement of the switch shaft with the tripped set of brushes 839, 840 and 84-1 in engagementwith the lowermost set of bank terminals in the selectedtrunk group. Relay 825 in releasing also establishes the previously traced circuit for advancing sequence switch 800 into position 7.

In position 7 of sequence switch 800, re-.

lay 825 is operated in a circuit extending from battery through its right Winding, the upper right contact of cam 842, lower right contact of cam 843, back contact of relay 856, commutator strip 85?, brush 858 to ground. Relay 825 energizes in this circuit closing a circuit for advancing sequence switch 800 into position 8. This circuit may be traced from battery through the winding of-magnet 800, upper right contact of cam 828, inner right front contact of relay 825, the outer left back contact of relay 802, to ground at the lower right contact of cam 807. In positions 7% to 8, relay 825 locks over its left-contact,

the right contacts of cam 845 to the test brush 839 and ground over the sleeve terminal of the trunk provided that trunk is busy. The original energizing circuit of relay 825 is opened when the sequence switch leaves position 7 If the first trunk of the group is bus however rela 825 is held energized in the right contacts of cam 842, commutator strip 8%, brush 847, the upper right and lower left contacts of cam 832, the inner right front contact of relay 825, thence to ground as traced. As soon as an idle trunk is reached characterized by the absence of ground on its sleeve terminal, the locking circuit of relay 825 is opened and that relay releases, in turn, releasing the updrive' magnet 831 to bring the nistrict selector to rest with its brushes 839, 840 and 841 on the terminals of the, selected idle trunk. The release of relay 825 closes a circuit from battery throughthe winding of sequence switch magnet 800, the right contacts of cam 83%, the inner right back contact of relay 825 to ground as traced for advancing sequence switch 800' into position 9.

As soon as relay 825 releases ground is connected to sleeve brush 839, over the upper contacts of cam 848, the outer right back contact of relay 825 to ground at the upper left contactof cam 833. As soon as the sequence switch arrivesin position 8% ground is connected over the lower right and upper left contacts of cam 8&8 to sleeve brush 839 independent of relay 825 which ground is mai.n tained until the sequence switch leaves position 15%. 7

With sequence switch 800 in position 9, a circuit is completed from battery through the right winding of relay 825, the lower left contact of cam8 i-t, the right front contact of relay 821 to ground at the upper right contact of cam 836. Relay 825 operates and closes a circuit from battery through the winding of sequence switch magnet 800, upper right contact of cam 826, inner right front contact of. relay 825 to ground astraced for advancing sequence switch 800 into position 10, in which position it remains until all subsequent selections are completed. In this position the fundamental circuit over which subsequent selections are controlled extends from brush 841, over the upper left and lower right contacts of cam 8&9, the rightback contact of relay 850, thence as traced over conductor 87 8 to the sender returning over terminal "1039, brush 1038, the upper left and lower right contacts of cam 1005, brush 1006, terninal 1007, conductor 818, th lower con tacts of cam 851 to brush Following the completion of units selection and the advance of the incoming selector, current over the fundamental circuit is reversed and the sender is prepared for making talking selection. At this time the sender increases the resistance in the circuit of relay 821 to such an extent that it releases, opening the circuit of relay 825 which in turn releases, closing a circuit from battery through the winding of sequence switch 1nagnet 800, over the right contacts of cam 834, the inner right back contact of relay 825 to ground as traced for advancing sequence switch 800 out of position 10 into position 11. As soon as sequence switch 800 reaches position 11 a circuit is closed for magnet 800 over the upper right contact of cam 826, the lower left and upper right contacts of cam 832, to ground at the rightcontact of earn 833 for advancing sequence switch 800 into position 12.

With sequence switch 800 in position 11, a local circuit is established for relay 821 extending from battery through the winding of relay 821, the right contacts of cam 820 to ground at the lower left contact of cam 836, and ground is connected to the sender over the lower left Contact of cam 836, conductor 819, terminal 1033, brush 1032, upper contacts of com 1046, left winding of relay 1015, left back contact of relay 1009, the u per right contact of cam 1034, brush 1031, terminal 1030 to battery in the sender for advancing the sender for making talking selection. Belay 1015 does not, however, opcrate in this circuit. At this time the calling line is connected over the lower contact of cam 815, through the left windings of repeating coil 852, the upper contact of cam 818, through the winding of supervisory rei lay 827, thereby ope-rat ng relay 827 which establishes a holding circuit for relay 821 oz:- tcnding from battery through the winding of relay 821, the front contact of relay 827 to ground a; the upper leftcontact of car-a Thus, relay 821 is maintained operated until the calling subscriber releases the connection.

In position 12 a circuit is established for relay 825 extending from battery through the left winding thereof, the lower left contact of earn 824, the upper left contact of cam 823,

conductor 878, thence as traced through the winding of the stepping relay of the sender to ground. Relay 825 and the stepping relay of the sender operate in this circuit, relay 825 closing the previously traced circuit for advancing sequence switch 800 out of posi tion 12 and locking itself to the fundamental circuit over its outer right front contact and the upper right contact ofcam 824. Switch 800 now advances under the control of relay 825 and in positions 12%, 13% and 14%connects ground over the right contacts of cam 48 in shunt of the winding of the sender stepping relay. The position in which sequence switch 800 comes to rest is determined by the counting relays of the sender in accordance with the talking selection registration set up by the sender code registers. .Vhen the sender is satisfied for this selection the fundamental circuit is opened thereby releasing relay 825 and stopping the sequence switch 800 in the next stopping position. For the purposes of this description it will be assumed that sequence switch 800 stops in position 14. In this position the right windings of repeating coil 852 are connected over the left contacts of cam 849 and left contacts of cam 851 to the brushes 841 and 840, respectively, in series over the left contacts of cam 845 and the winding of polarized relay 853, and thence to the repeatin g coil in the incoming selector.

The called line is tested by the final selector and if found idle, ringing current is applied from the incoming selector in the usual manner. WVhen the called subscriber answers relay 853 operates and as soon as interrupter 854 closes its lower contact it establishes a circuit for relay 802 extending from battery through the winding of relay 802, the lower contact of interrupter 854, left contacts of cam 842, front contact of relay 853 to ground at the upper left contact of cam 807. Relay 802 operates and looks over its inner left front contact, the lower contact of relay 808, the upper left contact of cam 843, the upper left contact of cam 842, front contact of relay 853 to ground at the upper left contact of cam 807. The operation of relay 802 prepares a circuit for relay 850 which may be traced from battery through the winding of relay 850,11pper left contactof cam 806, outer left front contact of relay 802, upper contact of interrupter 854 as soon as the interrupter advances to close its upper contact, the left contacts of cam 842, the front contact of relay 853 to ground at the upper left contact of cam 807. Relay 850, upon operating, locks over its inner left front contact to ground at the upper right contact of cam 807, closes a circuit from battery over its outer left contact, the contact of key 855, to ground through the winding of relay 810 and at its intermediate left contact establishes a new holding circuit for relay 870.

Relay 810, upon operating, reverses the connection of trunk conductors 504 and 505 to battery and ground through the left windings of repeating coil 852, thereby causing current to flow over the interoffice trunk through the windings of polarized relay 528 in such a direction as to operate this relay. Relay 528, upon operating, closes circuits in parallel for relays 526 and 533. The circuit of relay 533 which is quick operating but slow to release extending from battery, over the left back contact of relay 526, winding of relay 533, front contact of relay 528, front contact of relay 502, commutator strip 517,

brushes 518 and 510, strip 511 to ground at the lower front contact of relay 507. The circuit of relay 526 extends from battery through the winding of this relay to the contacts of relay528, thence to ground as just traced. Relay 526 being slow to operate does not operate as quickly as relay 533, thereby allowing relay 533 to operate and establish the obvious circuit for slow-to-release relay 534. Relay 534, upon operating, opens at its normal contacts the circuit hereinbefore traced from ground at the lower con tact of relay 507, through the winding of the calling line message register 118 to ground. As soon as relay 526 operates it opens at its left back contact the circuit of relay 533, at its inner right front contact closes a locking circuit for itself extending over the front contact of relay 502 to ground at the lower contact of relay 507 and establishes an operating circuit for the message register 118 extending from battery at its left front contact, over the alternate contacts of relay 534, the outer right alternate contacts of relay 526, the left front contact of relay 514, brush 521, terminal 522, the left back contact of relay 101 to ground through the winding of register magnet 118. This circuit is maintained only for the period required for slow-releasing relays 533 and 534 to release. As soon as relay 534 releases battery potential is removed from the operating circuit of magnet 118 and ground over the normal contacts of relay 534, the front contact of relay 502, over the circuit previously traced to the lower contact of relay 507 is substituted therefor, thus insuring that the message register will be operated but once.

After talking selection is completed the current in the circuit previously traced through the left winding of relay 1015 is increased to such an extent that relay 1015 operates and closes a circuit from battery through the right winding of relay 1017, the left contacts of cam 1021 to ground at the right front contact of relay 1015. Relay 1017 closes a circuit from battery through the winding of sequence switch magnet 1000, upper contact of cam 1079, outer right con tact of relay 1017 to ground at the right back contact of relay 1009, advancing sequence switch 1000 into position In this position all the conductors extendlng to the sender are opened and the sender is completely released.

As soon as sequence switch 1000 leaves position 5, relay 1015 releases and in turn releases relay 1017. With relay 1017 released in position 6, a circuit is closed from battery through the winding of sequence switch magnet 1000, lower left contact of cam 1076, left back contact of relay 1017 to ground at the lower left contact of cam 1016 advancing sequence switch 1000 into position 7. If another district is standing in position 1 awaiting association with a link, a circuit will be closed from ground over the lower left contact of cam 836, the lower contacts of cam 820, jack contacts 868, conductor 860, contacts of jacks 1048 and 1049 upper contact of cam 1016, left back contact of relay 1015, right contacts ofcam 1014 to battery through the winding of relay 1013. Relay 1013 closes a circuit'from battery, through the right winding of relay 1017, right front contact of relay 1013 to ground at the right back contact of relay 1015. Relay 1017 in operating closes a circuit for updrive magnet 1047 of the district finder 1010, lower right contact of cams 1079, outer right contact of relay 1017 to ground at the right back contact of relay 1009. The district finder moves upwardly under the control of magnet 1047 in search of a district which is in condition tobe seized. Such a district is identified by battery connected over the right contacts of cam 859, jack contacts 869, conductor 1091 to terminal 1050. Relay 1013, in operating, closes the same circuitthrough the right and middle windings of relay 1015 as it closedin position 2. At this time the test circuit extends to ground at the inner right front contact of relay 1013, through the right winding of relay 1015, upper left and lower right contacts of cam 1021, left winding of'relay 1015, left back contact of'relay 1009, upper right and lower left contacts of cam 1019, contact of jack 1049 to brush 1051. Relay 1015 thereupon quickly operates locking through its middle winding, the upper contacts of cam 1021 to ground at the right front contact of relay 1015, opening the circuit of relay 1017 to release magnet 1047 and bring the district finder to rest on the terminals of the district, and at its left back contact opening, the circuit, of relay 1013 which also releases. Since key 873 of each district of the frame which is not arranged for use with a line finder of ofiice A is operated, the link 1099 and all other links of the same group 1099.1099 will not be able to select such districts since the test terminals corresponding to terminal 1050 will thus be disconnected. With relay 1015 operated and relays'1013 and 1017 released, a circuit is closed from battery, through the winding of sequence switch magnet 1000, upper left contact of cam 107 6, contact 1027 of jack 1028, left back contact of relay 1013, left front contact ofrelay 1015, upper contact of cam 1016, contacts of jacks 1049 and 1048, conductor 860, jack contacts 868, the lower left contact of cam 820 to ground at the lower left contact of cam 836. Sequence switch 1000 advances to position 8 in this circuit.

Relay 1015 is held operated in position 8 from battery at the district selector over con- 

